Clamshell packages consist of a bottom portion (cup) capable of holding material to be enclosed in the package and a top portion (lid) hinged to one side of the bottom portion. The top portion folds over the bottom portion and the two portions are locked or press fitted to each other at their outer edges generally by pressure applied to the top portion. The name of the package is derived from its similarity to a clamshell. Since the package is simple in construction it provides a very economical and convenient means for enclosing, stacking, storing, shipping and dispensing many materials such as food products. Blueberries, strawberries and cherries are typical examples of foods that are commonly packaged in clamshell containers. If the package is made out of a transparent material such as a thin flexible plastic such as polyethylene tetrafluoride, the contents can also be attractively displayed. The package is designed to be readily opened and reclosed manually so the contents can be removed in whole or in part and the package can be reused if desired. The packages are available in various sizes with various closing mechanisms, the only limitation on the latter feature for purposes of the present invention is the ability of the top portion or lid to snap or press shut snugly over the bottom portion or cup by applying pressure on the top surface of the lid.
The prior art contains several examples of processes and machines for closing clamshell packages. It also contains several examples of processes and machines for closing cartons, boxes and other packages utilizing mechanisms similar to some of the mechanisms of the present invention. However, none disclose an automated process or machine that is designed to orient a package so that the hinge of the part being closed is on the trailing edge of the package with respect to the direction the package is traveling on a conveyer belt during the process of closing. The hinge orientation of the present invention closes the package with the hinge instead of against it. Other features of the present invention not shown in the prior art include the turning mechanism employed, the slightly faster speed of the top belt as it applies pressure to the clamshell container lid as the container moves along a conveyer and the ability of the lid to fit snugly over the bottom portion of the container by the simple application of pressure. These and other novel features in combination unexpectedly lead to almost 100% closure of the package at a faster speed than previous machines employed for the same purpose.
U.S. Pat. Nos. 2,224,716 2,927,411 3,267,637 3,443,353 4,590,745 and 4,672,792 are examples of patents that disclose box or carton closing machines having some mechanisms similar to that of the present invention. They differ in providing closing mechanisms that close cartons with hinged tops with at least three flaps that are attached to the carton body with adhesives or locking tabs. U.S. Pat. No. 2,971,443 is very similar except that hinged top to be closed has only a front flap attached with adhesive to the body of the carton. U.S. Pat. Nos. 2,242,304 4,722,176 and 5,249,406 are examples of patents that disclose clamshell closing machines but do not disclose closing mechanisms similar to that of the present invention. U.S. Pat. No. 5,092,108 discloses a mechanism for closing a two piece carton, i.e., a carton whose top is not hinged to the body of the carton. U.S. Pat. No. 3,015,198 discloses a mechanism for closing a conventional carton, i.e., one whose top and bottom has four hinged flaps with opposed pairs of transverse inner flaps and longitudinal outer flaps. None of these patents alone or in combination disclose mechanisms adapted to close the package with the hinged portion of the package trailing the package as it moves through the closing mechanism of the machine. None of these patents disclose a top belt that effects more efficient closure by moving at a slightly faster speed than the conveyer employed to move the package under the top belt. None of these patents disclose mechanisms that close packages or containers where the top is adapted to fit snugly over the bottom by the simple application of pressure on the top. Most include mechanisms that apply adhesives, lock hooks, interlock tabs or press buttons into wells to effect closure.